Epidemiologic studies have established an association between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and altered B cell function including, suppression of humoral immunity and increased incidence of non-Hodgkin's lymphoma. TCDD is ubiquitous, highly stable, lipophilic environmental contaminants that impair plasma cell formation. The overall goal of this five-year research plan is to test the Hypothesis: Impaired human B cell function by TCDD is mediated through sustained elevation of BCL6 in activated B cells. This sustained elevation in BCL6 promotes anergy and cell death in the majority of TCDD-affected B cells and impaired differentiation in a smaller population of TCDD-affected but surviving B cells. Next to induction of certain cytochrome P-450 drug metabolizing isozymes, suppression of primary humoral immune responses by impairment of plasma cell formation is one of the most sensitive sequela produced by TCDD, and has been demonstrated in virtually every animal species investigated. During the existing project period, one of the most significant advancement has been the demonstration that in the majority of human donors evaluated, human primary B (HPB) cells exhibited similar sensitivity to TCDD as B cells from TCDD responsive mouse strains (e.g., C57Bl/6) in spite of the fact that the human aryl hydrocarbon receptor (AHR) has approximately ten-fold lower affinity for TCDD than the mouse AHR. The direct effects of TCDD on HPB cell function represents a longstanding data gap, which we have begun to address and will continue in this competing renewal application. Moreover our results show, that in addition to decreased numbers of IgM secreting cells, TCDD- treatment caused elevated and sustained levels of BCL6, and decreased levels of CD80, CD69, pERK, p- p65/NF?B, and p-cJun, which are hallmarks of impaired B cell activation. Based on the above findings, a multifaceted cellular and molecular approach will be used to test our hypothesis using human primary B cells with the following specific aims (SA): SA1 is to determine the molecular mechanism responsible for impaired BCL6 down-regulation by TCDD in activated HPB cells; SA2 is to determine the role of TCDD-mediated induction of SHP-1 on suppression of B cell activation and function; SA3 is to establish the role of NFkB, AP-1 and BCL6 in TCDD-mediated impairment of CD80 up-regulation, a hallmark of altered B cell activation; and SA4 is to determine whether TCDD induces B cell anergy or an anergy-like phenotype. The significance of the proposed studies is that they will for the first time provide new and important information concerning the molecular mechanisms by which TCDD impairs human primary B cell function as well as offer new insights on how TCDD might contribute to the increased incidence of non-Hodgkin's lymphoma. Finally, the proposed experiments will provide new knowledge concerning the fundamental role of the AHR in B cell immunobiology.